Glossary

Cornea - The clear layer of tissue, shaped like a dome, that lies on top of the iris and the pupil. The cornea is the eye’s outer lens. It gives the eye its major focusing ability.

Epiretinal Prosthesis – An implant that is placed on top of the retina versus a “subretinal” that sits underneath the retina.

Fovea - The center of the macula; it gives the clearest vision and is used in reading.

Iris - The iris is the round structure in the eye that gives someone his or her eye color. For example, blue-eyed people have a blue iris while brown eyed people have a brown iris. The center of the iris is an opening called the pupil. The iris controls the size of the pupil when it reacts to the amount of light that is present.

Lens - A clear disc in the eye located behind the iris that helps focus light or an image on the retina.

Macula - The small, sensitive area of the retina that provides central vision. It is located in the center of the retina and contains the fovea.

Optic Nerve - A bundle of more than one million nerve fibers that carry visual messages from the retina to the brain.

Pupil – A hole in the center of the iris that allows light to enter the eye and reach the retina.

Photoreceptors - Cells in the retina that connect with other nerve cells to transmit visual information to the brain. Rod photoreceptors control night vision while cone photoreceptors are involved in color vision.

Retina - A thin layer of cells at the back of the eyeball that convert light into nerve impulses that travel to the brain.

Retinitis Pigmentosa - Retinitis pigmentosa (RP) is an eye disease which causes damage to the retina. This damage results in a loss of vision. RP can be caused by a genetic defect which will cause it to run in families. Early symptoms of the disease often are first experienced in childhood (loss of the ability to see at night or in very low light). Later the disease may lead to blurring of vision, tunnel vision, loss of central vision or loss of the ability to see colors. In many cases, these severe vision problems do not occur until early adulthood. In advanced stages of the disease, RP can lead to a person being able to see only very bright flashes of light. In the worst case, the person may experience total blindness.

Credit: National Eye Institute, National Institutes of Health for certain glossary terms